I think it's broken

Question

I have an AD2 that I use a lot and today the Channel 1 started showing an input voltage of -21 with nothing connected. Channel 2 and all other functions work great.

I restarted the computer, updated the software, and power cycled the AD2. No change.

I calibrated the waveform generator and then the scope, but scope calibration failed saying that Channel 1 is showing too high on the input when grounded. I tried reverting to the factory calibration, but the symptoms remained the same.

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You were correct, attila, it was the mux. After confirming with measurements, I cut pins 10 and 15 to be double-sure it wasn't the buffer.

I'm ordering anther ADG612 now.

After going over all my measurements and checking everything I did, I am confident that I did not damage the mux. I don't have anything over 9 volts on the bench, and I did not have a mis-matched ground problem anywhere. It just died of its own accord.

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My AD2 will not go down from +20 volts. I was doing some measurements with a transformer and the BNC kit for the AD2 and after some measurements, it looks like I also broke my Channel 2 input. The probes were x10 in the attenuation department.

Will the solution suggested work also for me? I have almost the same issue but is not -21, is +21.

The device works well measuring frequencies, the attached image shows the generator connected to channel 2, measuring 10 MHz.

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I think I did the measurements but not sure if I did them in the right manner.

My setup:

-OSC1 ----> GND

+OSC1 ----> to test points

Did all measurements with respect to GND of the AD2. In the last measurement I remembered that it also could have been differential measurements. Did all the differential measurements and the result is the same with the other two with respect to GND of the AD2.

I had to modify the +2.5 offset with 0.5 scale because the measurement will not show it self (higher than 0 volts I guess).

This was the VREF_SC2, with respect to GND it was close to 2 volts.

This one is the NETC410_1 with respect to GND. It was 1.1947v

This one is the diferential measurement, just took it after I´ve finished...

This one is the VOFF with 0 volts offset. It was almost 2 volts (1.9969)

This one is NET409_1 with 0 volts Offset respect to GND. It was 0.5855 volts.

This one is VOFF with -2.5 volts offset and 0.5 volts/div. It measures 1.99 volts.

This one is NETC409_1 with -2.5 volts offset with 0.5 volts/div. It measures 0.5786 volts.

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I meant measuring the VOFF_SC2 relative to the device GND with external DMM.
Having the scope channel 2 range 500mV/div or lower, changing the offset between -2.5V and 2.5V should change the VOFF_SC2 between ~1V and ~3V
Above 500mV/div for offset between -25V and +25V change VOFF between ~1V and ~3V.

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I meant measuring the VOFF_SC2 relative to the device GND with external DMM.
Having the scope channel 2 range 500mV/div or lower, changing the offset between -2.5V and 2.5V should change the VOFF_SC2 between ~1V and ~3V
Above 500mV/div for offset between -25V and +25V change VOFF between ~1V and ~3V.

Oh.... sorry, did not understad that.

Did the measurements. They are within range:

VREF2V = 0V

VOFF_SC2 with 0V offset = 1.94V,

VOFF_SC2 with 2.5V offset = 2.99V

VOFF_SC2 with -2.5V offset = 1.01V

All measurementes respecto to the device´s ground and with 500mV/Div for channel 2.

Edited February 21 by CamarilloDefinded the voltages.

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I almost forgot that odd reading or output offset could be due to wrong calibration.
Since the offset voltage is applied this it likely good, but please perform a "Load factory" and see the oscilloscope readings again to make sure the calibration is not culprit.

Otherwise the 21V reading is likely due to damaged ADG612.
The one for channel 2 is on the right side, the 16pin IC above the trimmers.

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Did the factory reset but the measurementes were the same. Although something happended that I did not notice: if I start channel 2 with the 500mV/Div, if i change it to 5V/Div, the signal from channel 2 goes to -3V and after a few seconds, it goes to +21 (with nothing conected to the probes).

Did a calibration after loading the factory data. The waveform channel, both 1 and 2 passed. But the oscilloscope did not, and it showed the behaviour described above (-2.7 volts to +21 volts.

Do you think it might be the MUX ADG612?

Thanks.

Edited February 24 by CamarilloDeleted the same image. Uploaded it twice.